1. Field of the Invention
This invention relates to castable polyurethane elastomers which are chain extended with diols, and, more particularly, with polyurethane polymers which are chain extended with 2,3-bis(hydroxymethyl)bicyclo[2,2,1] heptane (BHMCH), to provide advantageous physical properties, particularly low rebound characteristics, for use in shock absorber and anti-vibration mounting applications.
2. Description of the Prior Art
Polyurethane compositions obtained by curing liquid isocyanate-terminated prepolymers are finding increased use in diverse applications requiring castable elastomers. Because of their inherent toughness, outstanding resistance to abrasion, oils, solvents, chemicals, oxidation, and the wide range of hardness and flexibility from soft, flexible elastomers to rigid plastic, they are frequently used in numerous applications such as: abrasion resistant coatings; coatings on metal or fabric for belting; flexible mechanical couplings, gears and drive wheels; mallet and hammer heads; rollers for printing and feed conveying; shock absorbent pads and bumpers; solid industrial truck tires and caster wheels; and the like.
The polyurethane elastomers are linear multiblock copolymers of the (AB).sub.x type structure. They are typically formed as the reaction product of a diisocyanate with a hydroxyl terminated polyether or polyester polyol and a low molecular weight chain extender. The elastomeric properties of these materials arise from phase separation which leads to the formation of hard and soft segments. The soft segment consists of a long polyether or polyester chain with a molecular weight in the range of 1000-2000 while the hard segments are derived from the diisocyanate (MDI, i.e. 4,4'-diphenylmethane diisocyanate or TDI, i.e. tolylene diisocyanate) and low molecular weight chain extenders.
The most commonly used chain extenders for castable polyurethane elastomers are short chain diols, e.g. 1,4-butanediol (B.sub.1 D), cis-butenediol (cis-B.sub.2 D), transbutenediol (trans-B.sub.2 D) and butynediol (B.sub.3 D). See Lin, I. et al. "C.sub.4 -Diol Chain Extenders in Castable and Rim Urethanes", J. Elastomers and Plastics 15, 57-80 (1983).
U.S. Pat. No. 3,492,330 describes the preparation of substituted norboranes for use in the manufacture of polymers. The substituted norborane compounds were made by free radical addition of a functionally substituted alkane to the unsaturated carbon atoms of a bridged-ring olefin. Among the bridged-ring olefins listed therein was the unsaturated diol produced by a Diels-Alder reaction between cyclopentadiene and butenediol. Subsequent reaction of the unsaturated diol with a functionally substituted alkane at the position of unsaturation produced the desired substituted norborane. However, there was no description of a corresponding saturated diol (BHMCH) or of its use as a chain extending agent in the manufacture of new and useful castable polyurethane elastomers.
Birch, S. et al. in the J. Org. Chem. 21, 970-974 (1956) described the preparation of BHMCH by a three-step process. The disclosed process comprised a Diels-Alder condensation of cyclopentadiene and maleic anhydride to form an unsaturated anhydride, reduction of the anhydride with lithium aluminum hydride to produce the unsaturated diol, and hydrogenation of the ethylenic bond to produce the saturated diol, i.e. BHMCH. However, BHMCH was used merely to provide the corresponding sulfur analogs.
Accordingly, there is a need for novel castable polyurethane elastomers having advantageous physical properties which are products of polyurethane prepolymers and derivatives of short chain diols, in particular, derivatives of C.sub.4 -diols, for use as chain extenders of polyurethane prepolymers.
An object of this invention, therefore, is to provide such advantageous castable polyurethane elastomers.
A specific object herein is to provide castable polyurethane elastomers having low rebound properties for use in shock absorbant pads and anti-vibration mounting applications.